To measure the effect of laser fluence and scanning velocity on ablation efficiency of enamel and dentin.Two extracted human incisors and two molars were cut transversely along the axial plane with a diamond saw to obtain dentin and enamel slices with thickness of about 1 mm. Samples were fixed on a motorized translation stage, the linear reciprocating movement in the plane perpendicular to the direction of laser incident was programmed by the controller, and the laser focused on the tooth surface, then 36 ablation lines on enamel and 48 ablation lines on dentin were produced. A femtosecond laser system with wavelength of 800 nm, pulse width 30 fs, repetition frequency 1000 Hz was used, and the diameter of the focused spot was approximately 25 µm. A group of different fluence (1.33, 1.77, 2.21, 4.42, 8.85, 17.69 J/cm(2) for enamel and 0.44, 0.66, 0.88, 1.33, 1.77, 2.21, 4.42, 6.63 J/cm(2) for dentin) and two scanning velocity (10 mm/s and 20 mm/s) were tested. Confocal laser scanning microscope was used to measure the ablation volume.Ablation efficiency for enamel and dentin was then calculated.Under the fluence of 8.85 J/cm(2) there was the highest ablation efficiency for enamel, 18.703×10(-3) mm(3)/J (20 mm/s), and the highest ablation efficiency for dentin was found under the fluence of 2.21 J/cm(2), ie.223.458×10(-3) mm(3)/J (20 mm/s).Fluence and scanning speed of this femtosecond laser can affect ablation efficiency for both enamel and dentin, and this suggests that with appropriate choice of fluence and scanning speed we can improve the ablation efficiency for enamel and dentin.
The aim of this study was to evaluate the surface roughness and wettability of dentin following ultrashort pulsed laser ablation with different levels of fluence and pulse overlap (PO). Twenty-five extracted human teeth crowns were cut longitudinally into slices of approximately 1.5-mm thick and randomly divided into nine groups of five. Samples in groups 1 to 8 were ablated with an ultrashort pulsed laser through a galvanometric scanning system. Samples in group 9 were prepared using a mechanical rotary instrument. The surface roughness of samples from each group was then measured using a three-dimensional profile measurement laser microscope, and wettability was evaluated by measuring the contact angle of a drop of water on the prepared dentin surface using an optical contact angle measuring device. The results showed that both laser fluence and PO had an effect on dentin surface roughness. Specifically, a higher PO decreased dentin surface roughness and reduced the effect of high-laser fluence on decreasing the surface roughness in some groups. Furthermore, all ablated dentin showed a contact angle of approximately 0 deg, meaning that laser ablation significantly improved wettability. Adjustment of ultrashort pulsed laser parameters can, therefore, significantly alter dentin surface roughness and wettability.
Objective: Femtosecond laser (fs-laser) is a novel tooth preparation tool but its ablation efficiency is insufficient. The purpose is to establish a new fs-laser tooth ablation method based on a dual-wedges path ablation system, and explore the efficiency of tooth hard tissue and dental restorative materials ablation. Materials and methods: Extracted third molars, pure titanium, cobalt-chromium alloy, gold alloy, and 3Y-zirconia were prepared into samples. These samples were rotary ablated by an fs-laser with dual-wedges. The wavelength was 1030 nm and the pulse duration was 250 fsec. Laser parameters were set as a repetition frequency of 25 kHz, the power percentages as 50% for dental tissues, and 60% for restorative materials. The optical wedge angle was set as 0°, 20°, 40°, 60°, and 80° for restorative materials, 0°, 20°, 30°, 40°, and 60° for enamel, and 0°, 10°, 20°, 30°, and 40°for dentin. Three times of ablation was processed at each parameter to obtain total 90 ablation microcavities of 6 kinds of materials. The diameter, depth, and volume of microcavities were measured by confocal laser microscopy and plotted against optical-wedge-angle in curves of different materials. One-way analysis of variance (ANOVA) was used to test whether the ablation efficiency between different angles was statistically significant. Results: The ablation efficiency of each material at different optical-wedge-angle was statistically significant (p < 0.05) and tends to be correlated. For dental hard tissue, the enamel ablation efficiency was 208.1 times and dentin ablation efficiency were 65.2 times than before when the wedge angle was 40°. For pure titanium, zirconia, cobalt-chromium, and gold alloys, the ablation efficiencies were 3.1, 10.7, 81.5, and 128.8 times than before when the rotation angle was 80°. Conclusions: The ablation efficiency of dental hard tissues and restorative materials was significantly increased with the increase of laser oblique incidence angle. Clinical Trial Registration number: PKUSSIRB-201949124
Purpose The use of removable complete dentures is a selectable restorative procedure for edentulous patients. To improve the fabrication quality and efficiency of removable complete dentures, this paper aims to introduce a new method to fabricate customized wax complete dentures with additive manufacturing. This process uses complementary digital technologies, and allows faster and better manufacture of complete dentures. Design/methodology/approach In the study, a dental scanner was used to obtain surface data from edentulous casts and rims made by the dentist. A parameterized three-dimensional graphic database of artificial teeth was pre-established. Specialized computer-aided design software was used to set up the artificial dentition and design the esthetic gingiva and base plate. A selective laser sintering machine was used to transfer the data from stereolithography files into a wax base plate with location holes for each artificial tooth. Findings Under this method, a set of wax base plates with 28 location holes available for the placement of the artificial teeth were designed and fabricated within 6 h. The try-in wax dentures fitted the patient’s mouth well, besides occlusion relationships. Then, the occlusion relationships can be adjusted manually to achieve a balanced centric occlusion. Originality/value This method can be used to design and fabricate wax try-in removable complete dentures semi-automatically and rapidly; however, the algorithm for the occlusion contact design needs to be improved.
With the development of three-dimensional (3D) scanning and measurement technologies, the internal adaptation of restorations was measured by the 3D analysis method. The purpose of this study was to explore a novel 3D digital evaluation method to assess the intraoral fitness of removable partial dentures (RPDs) and evaluate the accuracy of this novel digital method in vitro. A 3D digital method to evaluate the clinical fitness of RPD was introduced. A standard stone cast of a partially edentulous mandible simulating the oral tissues and a corresponding RPD were used to evaluate the accuracy of this novel digital method (3D analysis on duplicated polyether cast) and another reported 3D digital evaluation method (3D analysis on RPD directly) for intraoral fitness of RPD in vitro. 12 polyvinyl siloxane (PVS) replica specimens were fabricated in each method in vitro, and the thicknesses of these PVS replicas were measured by 3D analysis on duplicated polyether cast (named Polyether group), 3D analysis on RPD directly (named Denture group), and 3D analysis on the stone cast (named Stone group), respectively. The thicknesses of PVS replicas were compared with analyses of variance (ANOVA) to evaluate the accuracy of these methods (α = 0.05). The accuracy based on the mean thickness of the PVS replicas of Polyether group were better than that of Denture group (P < 0.05) and had no statistical difference with that of Stone group (P > 0.05). 3D analysis on duplicated polyether cast has comparable trueness and precision to 3D analysis on the stone cast and is feasible for evaluating clinical fitness of RPD.
To design a hydrogel material containing nano hydroxyapatite particles for three-dimensional (3D) bio-printing and to explore whether nano hydroxyapatite particles can promote osteogenic differentiation of 3D bio-printing construct consisting of hASCs in vivo and in vitro.
The objective was to study the relationship between laser fluence and ablation efficiency of a femtosecond laser with a Gaussian-shaped pulse used to ablate dentin and enamel for prosthodontic tooth preparation. A diode-pumped thin-disk femtosecond laser with wavelength of 1025 nm and pulse width of 400 fs was used for the ablation of dentin and enamel. The laser spot was guided in a line on the dentin and enamel surfaces to form a groove-shaped ablation zone under a series of laser pulse energies. The width and volume of the ablated line were measured under a three-dimensional confocal microscope to calculate the ablation efficiency. Ablation efficiency for dentin reached a maximum value of 0.020 mm3∕J when the laser fluence was set at 6.51 J∕cm2. For enamel, the maximum ablation efficiency was 0.009 mm3∕J at a fluence of 7.59 J∕cm2.Ablation efficiency of the femtosecond laser on dentin and enamel is closely related to the laser fluence and may reach a maximum when the laser fluence is set to an appropriate value.
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